This type of inertization process is known in principle from the prior art. For example, German Patent Specification DE 198 11 851 C2 describes an inertization device for decreasing the risk of fire and for extinguishing fires in enclosed spaces, and a device for implementing said process. This prior art provides for the oxygen concentration inside an enclosed space (hereinafter called “protected room”) to be lowered to a specific base inertization level, and in the event of a fire for the oxygen concentration to be rapidly further decreased to a specific full inertization level, thereby enabling an effective extinguishing of a fire with the smallest possible storage capacity for inert gas tanks.
This inertization process is based upon the knowledge that inside enclosed spaces which humans and animals enter only occasionally, and in which the equipment reacts sensitively to the effects of water, the risk of fire can be countered by lowering the oxygen concentration in the relevant area to a level averaging approximately 12 vol.-%. At this oxygen concentration, most combustible materials can no longer burn. The main areas of application include especially ADP areas, electrical switching and distribution spaces, enclosed facilities, and storage areas containing high-value commercial goods.
The extinguishing effect resulting from this process is based upon the principle of oxygen displacement. As is known, normal environmental air is made up of 21 vol.-% oxygen, 78 vol.-% nitrogen and 1 vol.-% other gases. To extinguish a fire, the nitrogen concentration in the relevant space is further increased by introducing nitrogen, thereby decreasing the oxygen ratio. It is known that an extinguishing effect is initiated when the oxygen ratio drops below 15 vol.-%. Depending upon the combustible materials present in the protected room, a further drop in the oxygen ratio, for example to 12 vol.-%, may be necessary.
The term “base inertization level” used herein refers to an oxygen concentration that is reduced as compared with the oxygen concentration of the normal ambient air; however this reduced oxygen concentration presents no danger of any kind to persons or animals, so that these are still able to enter the protected room without problems. The base inertization level corresponds to an oxygen concentration inside the protected room of, for example, 15 vol.-%, 16 vol.-%, or 17 vol.-%.
In contrast, the term “full inertization level” refers to an oxygen concentration that is reduced further as compared with the oxygen concentration of the base inertization level, in which the flammability of most materials is already decreased so far, that they are no longer capable of igniting. Depending upon the fire load inside the protected room, the full inertization level generally ranges from 11 vol.-% to 12 vol.-% oxygen concentration.
In the “inert gas extinguishing technique” known from DE 198 11 851 C2, which refers to the flooding of a space that is prone to fire or is on fire with oxygen-displacing gases, such as carbon dioxide, nitrogen, noble gases and mixtures of these, the oxygen concentration inside the protected room is first lowered to a specific base inertization level of, for example, 16 vol.-%, and in the event of a fire is further lowered to a specific full inertization level of, for example, 12 vol.-% or lower. By using this two-stage inert gas process, in which first the base inertization level is established to reduce the risk of fire, and in which enough nitrogen is supplied, as needed, in an additional introduction of inert gas to extinguish a fire, until the full inertization level has been established, the result is that the number of tanks needed for the oxygen-displacing inert gases required in the event of a fire can be kept as small as possible. Especially, with this inertization process known from the prior art, the need to provide a relatively large storage capacity for inert gas tanks in order to be able to establish a full inertization level inside the protected room in the event of a fire is eliminated.
However, in the practical application of this known process, it has been found problematic, that with the inertization process in the event of a fire, in other words when a characteristic fire value has been detected in the atmosphere inside the protected room, the oxygen concentration inside the protected room must be lowered very rapidly to the specific full inertization level. This is accomplished by introducing the necessary volume of gas within a very short time into the protected room in the event of a fire, in order to effectively contribute to extinguishing the fire. Although the known and above-described process largely solves the problem of storing the inert gas tanks required to establish the full inertization level, it has nonetheless been found problematic that in establishing the full inertization level within the shortest period of time, a volume (although reduced) of inert gas must be introduced into the protected room, which frequently cannot be accomplished considering the necessary decompression of the protected room. The inflow of the reduced gas volume to establish the full inertization level is found to be especially problematic in protected rooms in which no structural decompression is provided.
Furthermore, the above-described prior art provides that, in the event of a fire, the oxygen concentration inside the protected room is lowered to the full inertization level, independent of the size of the fire and/or the type of fire, by releasing the total quantity of recommended extinguishing agent. In particular, with the prior art, no differentiation is given as to what stage the fire is in. Thus the full inertization level is established regardless of, whether, for example, a deep glowing fire is present or only a low-temperature fire, or what materials first ignited inside the protected room. For example, if only solids ignited inside the protected room, a full inertization of the protected room to approximately 14 vol.-% oxygen to combat the fire would be sufficient to effectively prevent an ignition of the solid, since the ignition threshold for solids lies at approximately 15 vol.-% oxygen. If, however, combustible fluids, which are known to have an ignition threshold below 15 vol.-%, caught fire inside the protected room, then full inertization for fighting the fire must be implemented to the aforementioned 12 vol.-% oxygen or lower.
With the known process, however, in principle a full inertization to, for example, the aforementioned 11 vol.-% oxygen is performed—regardless of the ignition threshold of the materials burning inside the protected room, so that under certain circumstances significantly more inert gas is supplied to the protected room than would be necessary to fight the fire.